[TG] [TG11] Autopilot looses course after about 5 minutes

[Tom - Raymarine - Moderator]

Hello Bambooboat,

The ST70 is fine to use with an S3G, but you won't see the same calibration options as you would with a more advanced SPX pilot.

All of the calibration is stored in the Course Computer (S3G) and so replacing the display will make no difference to the way the pilot steers. You ought to be able to calibrate via the ST70 (though it's been a lot of years since I have tried) but I wouldn't expect dumping everything and starting again. I don't think this is a simple calibration error.

• If you steer the boat in a series of slow circles whilst in Standby, what happens with the indicated pilot heading? Does it change smoothly, evenly, consistently to match the vessel's heading? Does it seem to lag behind, or drift, or count backwards at any time? If you take the grey plastic cover off the S3G and unplug the 3-core Rate Gyro cable on the left-hand side (red-yellow-black wires, white connector, power the S3G down first) and do the same circles, does the pilot heading seem to stick/freeze and then jump at any point? If you have any unusual heading behaviour, you have a problem Rate Gyro or fluxgate compass. If the problem is throughout 360 degrees or stops when you unplug the gyro, it's the gyro. If it's only in certain sectors or continues when the gyro is unplugged, it's the fluxgate.
• If you turn the helm very slowly port-starboard lock-to-lock several times and watch the rudder position indicator, does that ever flicker, disappear, stick, jump, count backwards? If so, you have a rudder reference fault.
• If you turn the helm far to port and then press Auto, does the drive move it positively and smoothly to centre each time you do this? Does it do the same to starboard? If you go into Auto and make lots of +10/-10 course changes, does it always do a firm, positive movement? If not, you probably have a motor or hydraulic problem.
  

If I had to take a guess based on limited info, I'd say either a failing pump motor or a broken winding in the fluxgate compass.

Regards,
Tom